1. Field of the Invention
This invention pertains to machining workpieces, and more particularly to apparatus that aids in hand drilling and tapping holes.
2. Description of the Prior Art
It is well known to drill and tap holes by hand. A great number of electric hand-held drills are in everyday use by both professional and amateur machinists and craftsmen. Similarly, hand tapping is a common practice.
A major problem associated with hand drilling is that of producing a hole such that its longitudinal axis is perpendicular to the workpiece surface in which the hole is drilled. Jigs and fixtures are commonly used to guide drills in production operations used in industry. However, such jigs and fixtures are of little use in solving the hand drilling problems faced by home craftsmen or even by professional machinists. With hand operations, the person frequently must rely only on his eye to properly align the drill both before and during the drilling operation. Inaccurate holes are frequently the result. The person may use a small square to initially align the drill. However, during the course of the actual drilling, the square is invariably removed from against the drill, leaving it free to wander in space and thereby produce an inaccurate hole.
The problems associated with hand tapping holes are at least as great as those associated with hand drilling. Even if the hole to be tapped is accurate, there is no assurance that the hole will be tapped in an acceptable manner. That is because, like a hand-held drill, a hand-held tap is also free to wander in space as it is rotated by the machinist. Unless the tap longitudinal axis is concentric with the hole longitudinal axis, the tap will break. It is well known that tap breakage is caused by misalignment between the hole and the tap, and not merely by the torque applied to the tap.
As in drilling operations, the machinist may use just his eye to align a tap, or he may employ a square. Even if the tap is initially aligned in a perfect fashion, however, as soon as the tap is rotated it tends to wander and thereby enter the hole in a misaligned fashion. The all-to-common result is a broken tap.
Thus, a need exists for improvement in hand drilling and tapping operations.